Apparatus for gaseous reduction of oxygen-containing copper

ABSTRACT

A novel tuyere design in which a metal pipe is secured to the furnace wall and into which a second pipe is inserted to extend for several inches into the molten bath. The apparatus for introducing a gas into a furnace includes an outer pipe secured in a furnace wall and extending from the inner face of the wall to at least the outer face, an inner pipe adapted to be slidably inserted into the outer pipe and being of substantially greater length than the outer pipe, and means for introducing a gas into the inner pipe.

United States Patent Vogt et al. 1 Mar. 21, 1972 [541 APPARATUS FOR GASEOUS 602,947 4/1898 Kelly et al ..266/41 REDUCTION OF OXYGEN- l,292,162 1/1919 Amburgh ..266/41 CONTAINING COPPER 1,793,849 2/1931 Gronlnger... .....266/4l 2,261,559 11/1941 Osborn ..266/41 [72] Inventors: John Vogt; Paul Schmidt, both of Noran- 2,333,654 11/ 1943 Lellep ..266/41 da; Leonard Mills, Murdochville, all of 3,084,924 4/ 1963 Morlock .266/36 H Quebec, Canada 3,397,878 8/1968 Holmes et al ..266l41 [73] Assignee: Noranda Mines Limited, Toronto, Ontario, FOREIGN PATENTS QR APPLICATIONS Canada 708,419 8/1952 Great Britain ..266/41 [22] Filed: Dec. 31, 1969 Primary ExaminerGerald A. Dost [2]] Appl' L917 Attorney-Stevens, Davis, Miller & Mosher Related US. Application Data [57] ABSTRACT [62] Division ofSer. No. 696,526, Jan. 9, 1968. I

A novel tuyere design in which a metal plpe ls secured to the 52 us. Cl. ..266/36 H, 266/41 furnace Wall and into which a Sewn! PilPe is inserted [51] int. Cl ..C21c 5/48 for Several inches into the molten bath- The apparatus for [58] Field of Search ..266/36 H 41 42- 110/1825- tmducing a gas into a furnace includes Outer Pipe Secured 75/75 in a furnace wall and extending from the inner face of the wall to at least the outer face, an inner pipe adapted to be slidably 56] References Cited inserted into the outer pipe and being of substantially greater length than the outer pipe, and means. for introducing a gas UNITED STATES PATENTS into the inner P p 599,668 2/1898 Beaghan ..l10/182.5 9 Claims, 6 Drawing Figures Patented March 21, 1972 Patented March 21, 1972 5 Sheets-Sheet 2 Patented March 21, 1972 3,650,519

5 SheathSheot 5 Patented March 21, 1972 3,650,519

5 Shoots-Shoot 4 Patented March 21, 1972 3,650,519

SShutI-Shut 5 APPARATUS FOR GASEOUS REDUCTION OF OXYGEN- CONTAINING COPPER This application is a division of application Ser. No. 696,526, filed Jan. 9, 1968.

This invention relates to the pyrometallurgical refining of molten copper by the consecutive steps of oxidation and reduction. More particularly it relates to apparatus for the removal of undesirable oxygen contained in the copper by the use of a gaseous reductant. Still more specifically the invention relates to the use of a gaseous reductant at relatively high pressures and to a novel tuyere design for the introduction of the gaseous reductant.

Copper has been pyrometallurgically refined for many hundreds of years by essentially unchanged methods. Agricola in De Re Metallica published in 1556 describes a process which has changed so little that the work could have been written in the twentieth century. Essentially the process involves the poling of a molten bath of copper with a pole of green timber in a reducing atmosphere. The pole is pushed below the surface of the molten copper where it causes violent agitation by the rapid evaporation of moisture and volatile matter from the green wood and forces the molten copper into a fountain in the highly reducing atmosphere maintained in the furnace.

Many workers have suggested alternatives to the poling procedure, which involves cumbersome, arduous and hot labor on the part of the operatives and which is expensive in view of the growing scarcity of suitable timber poles. Among the suggestions are the use of other reducing agents such as coal, charcoal, petroleum or manufactured reducing gases. One notable attempt to use natural gas is described in Journal of Metals", Aug. 1961, pp. 545-547 by Leonard Klein, wherein it was found that the reducing effect of natural gas on molten copper is small and intolerably slow. This failure led Klein and his co-workers to the conclusion that natural gas should be reformed to hydrogen and carbon monoxide before being introduced into the refining furnace. Several expensive reforming plants were built in association with copper refining facilities and a process which employs pressures up to about p.s.i.g. is fully described in U.S. Pat. No. 2,989,397 to Kuzell et al.,June 20,1961.

It has now, surprisingly, been found that copper may be economically refined to an acceptable metallurgical standard by unreformed natural gas when used according to the present invention.

In the practice of the present invention the reductant, which is preferably unreformed natural gas but which may also be propane, butane, pentane, ethane or other gaseous or liquid hydrocarbons either alone or in admixture with steam or air is injected at pressure in excess of 30 p.s.i.g. and at normal temperatures through a tuyere into the molten bath of copper.

Alternatively, a reductant gas at elevated temperatures is injected into a bath of molten copper through a tuyere at pressures up to about 30 p.s.i.g. In the apparatus of the present invention a novel tuyere is described which is suitable for the introduction of the reductant at the desired pressure conditions.

Without wishing to be bound by this explanation it is believed that when reductant gases are introduced to the bath at relatively high pressures with an attendant relatively high exit velocity, the large velocity and density differences between the gas jet and the liquid bath result in a high degree of instability and any large bubbles which are injected initially into the bath are shattered into very fine small bubbles. Consequently a high specific surface area is achieved and the heat and mass transfer as well as the chemical action between the gas and the liquid bath are very high. One result of this high heat transfer is that hydrocarbons such as methane (the principal constituent of natural gas) and propane, are very quickly pyrolized to hydrogen and carbon which react with the copper oxide in the melt. Therefore, it is possible to obtain a very high utilization efficiency of the gas during its relatively short residence time in the liquid bath. Also, the use of high pressure allows the reducing gas to be introduced at deeper depths below the surface face of the copper bath thereby giving the gas additional residence time in the melt. High velocity and deep immersion give better mixing which results in more efficient use of the reductant.

In the drawings which are illustrative of the present invention:

FIG. 1 is a section of a rotary copper refining furnace;

FIG. 2 is a section of a tuyere according to the prior art;

FIG. 3 is a section of an alternative tuyere according to the prior art;

FIG. 4 is a section of the tuyere according to the present invention;

FIG. 5 is a section of an alternative embodiment of the tuyere according to the present invention; and

FIG. 6 is a section of a furnace showing an extraction device for a tuyere of the present invention.

Referring now to FIGS. 1, 2 and 3 in detail, and according to the prior art, copper may be refined in cylindrical furnace, shown generally at 1 (FIG. 1) having a refractory brick lining 2. Molten copper 3 is introduced into the furnace via skimming and fill port 4 and the furnace is rotated so that the tuyere brick 5 and its associated tuyere pipe 6 is beneath the level of the molten copper, as shown in FIG. 2. Reducing gas is normally introduced to the furnace: via two tuyeres 6 and hoses 7, located one near each end of the furnace. FIG. 3 shows an alternative tuyere form in which an inner tuyere pipe 8 is inserted inside tuyere pipe 6. During operation molten copper freezes to a greater or lesser extent over the end of and up into the tuyeres at 12 and 13, thereby reducing the cross sectional area and the gas flow. This usually occurs gradually, the rate of plugging being a function of the depth of immersion and the amount of superheat in the copper. Usually, and probably several times during a refining cycle, it is necessary to rotate the furnace so that the tuyeres come out of the copper and to shut off the gas and unplug the tuyeres with a reaming bar and sledge hammer. Plugging of the end of the tuyeres and hence low gas flow results in overheating of the tuyere insert and thus leaves the pipe in a weakened condition. Repeated reaming often results in breaking off the weakened portion of pipe which may necessitate expensive and time consuming repairs.

A further problem with the prior art techniques is that of blow back, which may occur when a tuyere insert 8 becomes blocked or burns back to the face of the brick. Reducing gas flows between the large pipe 6 and the brick 5, and emerges to atmosphere around the pipe 6 at 9 or around the removable shell plate 10 at 11. In the tuyere of the type shown in FIG. 3, gas also flows around the swaged end 14 of the insert pipe 5, into the annular space 15 and hence finds its way back between pipe 6 and tuyere brick 5. The gas may ignite as it enters the atmosphere in which case an intense flame results which endangers the steel work and trailing rubber hoses 7. If the gases do not ignite there is a danger that explosive pockets of gas may form. In the present invention, an embodiment of which is shown in FIG. 4, the above disadvantages are overcome.

According to the present invention a rotary copper refining furnace comprises an outer highly heat resistant metal pipe of substantially similar length to the thickness of a refractory lining in said furnace and secured thereto, an inner pipe of highly heat resistant metal slidable into said outer pipe and extending beyond said outer pipe at both of its ends, and means adapted to connect a gas supply to the outer end of said inner pipe.

Referring to the drawings, an outer pipe 16 is grounded into a hole in the tuyere brick 17 by known techniques, open to atmosphere at 18. Pipe 16 may be made of any grade of steel, preferably stainless steel of such grades as type 309, 310 and 316, and for longest life type 446 ferritic stainless has been found most suitable. A second pipe 19 which can be of any convenient material such as black iron or mild steel but with an alloy extension 28 welded to the hot end, preferably of stainless steel such as type 446 ferritic, slides inside pipe 16 and actually carries the reducing gas via the pipe tee 20 and fitting 22 from hose 23 and the gas source (not shown). Pipe tee 20 is provided with a pipe plug 21 for cleanout and inspection purposes. Pipes 16 and 19 are selected so that they are convenient sliding fits, for example if pipe 16 is 1.380 inches I.D. then pipe 19 is conveniently 1.050 inches O.D. and if pipe 16 is 1 /16 inches I.D. then pipe 19 could be 1.66 inches O.D. Pipe 19 may be coated with a refractory material (such as the aluminum silicate mortar sold under the trademark KYANEX") to ensure a good fit and to prevent fusion of the two pipes during service. A spacer 25 is installed between the furnace wall and tee to prevent the tip 28 from projecting too far into the furnace. A chain 26 is also attached to tee 20 and the furnace shell to prevent the pipe 19 sliding out of pipe 16 through the jet action of the issuing gas or when the furnace is rotated. The hot end 28 of the pipe may extend to any length into the furnace beyond the hot wall face 27, but lengths in excess of 5 inches are unnecessary and may bend or result in premature burn out. If they bend upwardly the reductant will be directed toward the bath surface rather than the body of the bath. Preferably a length of 3-4 inches is maintained, inserting the pipe further as the end is burnt off. The pipe may be used until it becomes flush or slightly countersunk with the hot wall face 27, at which point the possibility of blowback occurs. A somewhat similar tuyere block has been described in Canadian Pat. No. 673,243 to Hall, 29 Oct., 1963, but in this reference the two pipes are maintained flush with the hot wall face'and the inner pipe does not extend into the furnace, and furthermore the two pipes become fused together in service to prevent blow back. The present invention specifically avoids the fusion of the two pipes as this prevents relative movement between the two pipes.

In operation the tuyeres 19 are inserted to extend about 34 inches into the furnace and the furnace is filled to within about 2or 3 inches of the tuyere pipe as in FIG. 1. An appropriate gas, for .either an oxidizing or reducing reaction is then introduced through the tuyeres and the furnace is slowly rotated until the tuyere tip 28 is submerged below the surface of the molten copper. The depth to which the tip is submerged depends somewhat on the operating pressures available and may be any depth up to about 30-36 inches. Initially it is possible that some liquid copper flows into the annular space 31 between the inner and outer pipes and freezes to form a solid seal 29. This seal may help to prevent blow back but is not considered essential or even important, as the pipe diameters are closely matched and any copper which does so freeze is minor, and does not prevent later relative movement between the pipes 16 and 19. As the pipe 19 burns back, the spacer can be removed and pipe 19 advanced 3 or 4 inches into the furnace and a shorter spacer inserted. This process may be repeated until all of the tip 28 has been consumed.

When a tuyere of this design is employed the possibility of blow back is almost eliminated and relatively high gas pressures may be employed, as will be discussed hereinafter. The need for reaming the tuyere during the refining cycle is virtually eliminated as the high pressure gas prevents copper from splashing back into the tuyere and freezing and hence eliminates blocking. A greatly increased gas flow is achieved which does not fall off significantly with a gradually blocking tuyere and this makes it possible to operate with a single tuyere rather than two. Furthermore it is not necessary to begin with shallow submersion when the copper is cold, as when low gas pressure is used, in order to reduce the tendency of the tuyere to plug.

It is emphasized that this invention is capable of using reductants at high pressures with the use of the tuyere described herein. Gas pressures, using natural gas, up to about 100 p.s.i.g. have been used with a tip immersion of about inches, and higher pressures and deeper immersions could be employed, depending on the availability of high pressure gas handling equipment. Pressures as low as about 15 p.s.i. can be used for reductants other than methane. It has been found that at low pressures the time for complete reduction is prolonged so that normally pressures in excess of about 30 p.s.i.g. are employed. If low pressures of the order 715 p.s.i.g. are employed, preheating of the reductant gas improves the reaction rate and efficiency of gas utilization.

EXAMPLE 1 A 13 feet X 30 feet anode furnace was charged with 250300 tons of copper, and deoxidized using gaseous propane admixed with steam injected through one tuyere at a line pressure of 70 p.s.i.. with l00-l50c.f.m. and a tuyere immersion of about 30 inches a high turbulence was created in the bath resulting in exceptionally high efficiency in reducing gas utilization. The charge was completely deoxidized in 80-100 minutes, and required 1.12 gallons of propane per ton of copper which compares more than favorably with the usual 1.65 gallons/ton reported by smelters employing low pressure propane.

As previously indicated unreformed natural gas is a preferred reductant as it has a number of practical advantages over propane or other manufactured reductants including:

a. lower cost only about one third of the cost of propane per ton of copper refined; b. ready availability at many smelter sites, particularly in North America;

c. simplified piping and control system;

d. difficulties stemming from (b) storage tanks, pumps, and

Vaporizers are eliminated;

e. use of natural gas according to the present invention eliminates the requirement for a propane vaporizer or natural gas reformer, which represents a major capital saving; and

. the volume of objectionable black smoke, normally generated when deoxidizing with propane, is substantially reduced.

The following examples illustrate the efficiency of natural gas operations.

EXAMPLE 2 A visual check of the single three-quarter-inch 446 stainless steel tip used in the furnace of Example 1 was made to insure that it extended at least one-half inch into the bath and preferably 2-3 inches. The furnace was then charged with copper and oxidized by blowing air at 45 p.s.i.g. into the bath through the submerged tuyere. Slag was skimmed as necessary and samples taken until the visual observation of a sample revealed complete removal of sulphur. This took about 20 minutes at a bath temperature of 2,250 F.

The refining stage was then started by substituting the air supply to the tuyere with natural gas. The tuyere was maintained at about 30 inches below the copper bath surface during the refining stage and the heating burner was turned off. Natural gas was injected at 370 c.f.m. for 90 minutes and then the flow was reduced to 325 c.f.m. for 20 minutes at a supply line pressure of p.s.i.g. and an inlet tuyere pressure of 65 p.s.i.g. TI-le temperature at the end of the refining stage was 2,160 F. Steam was also injected mixed together with methane at 85 c.f.m. for minutes and c.f.m. for 20 minutes.

It was estimated that at the end of the oxidizing stage that the oxygen content of the copper was 0.83 percent and at the end of the refining stage 0.1 percent. With a production of 290 tons of anode copper and a total natural gas consumption of 41,236 cu. ft. this represents a consumption rate of 142 cu.ft./ton and an efficiency of 63.4 percent based on a theoretical rate of 90 ft. /ton.

EXAMPLE 3 The same procedure to that of Example 2 was carried out under similar conditions of bath temperatures and gas pressures. The bath was oxidized and skimmed for 30 minutes to yield a blister copper having an oxygen content of 0.85 percent. Natural gas was then injected at 240 c.f.m. and 85 p.s.i.g. line pressure (tuyere inlet pressure 65 p.s.i.g.), for minutes. Steam was also injected at 85 c.f.m. A total of 39,750

ft. of natural gas was consumed to produce 280 tons of anode copper which had an estimated oxygen content of 0.10 percent. Based on a theoretical consumption of 90 cu.ft./ton of anode copper produced, this utilization corresponds to an efficiency of 63.3 percent.

In carrying out Examples 2 and 3 it was observed that the volume of black smoke generated was much less than the serious and objectionable amounts generated in the test of Example 1.

EXAMPLE 4 In another run the bath was oxidized and skimmed for 30 minutes to yield a blister copper having an oxygen content of 0.85 percent. Natural gas was then injected at 430 c.f.m. and 85 p.s.i.g. line pressure (tuyere inlet pressure 65 p.s.i.g.), for 95 minutes. No steam was used in this run. A total of 38,450 ft. of natural gas was consumed to produce 270 tons of anode copper which had an estimated oxygen content of 0.10 percent. Based on a theoretical consumption of about 90 cu.ft./ton of anode copper produced, this utilization corresponds to an efficiency of about 63 percent.

The following Examples illustrate the effects of low pressures and preheated methane as the reductant.

EXAMPLE 5 In a laboratory experiment, a 230 lb. melt of anode copper, heated to 2,] 20 F. in an oil fired pot furnace was treated with commercially pure methane by injecting said gas 3.5 inches below the surface of the melt at a flowrate of 0.5 s.c.f.m. and a pressure of 2.7 p.s.i.g. The methane was preheated to or near the temperature of the melt by firstly passing it through a pipe of 1-inch nominal diameter, 2 to 3 feet of said pipe being sur rounded and heated by the hot flue gases of the furnace. It was found that the oxygen content decreased from 0.65 to 0.53 percent oxygen (W/W) during a period of 2.3 minutes of the above treatment.

EXAMPLE 6 In another experiment similar to example 5 but injecting the methane 5.9 inches below the surface of the melt at a pressure of 3.2 p.s.i.g. all other conditions remaining the same, the oxygen content in the copper melt was found to decrease from 0.53 percent oxygen to 0.10 percent oxygen during a period of 9.1 minutes ofsaid treatment.

EXAMPLE 7 In still another experiment the gases issuing from the melt were analyzed while a 270 lb. melt of copper, containing 0.55 percent oxygen (W/W) was undergoing a similar treatment. Methane was injected 3.2 inches below the surface at a fiowrate of 0.89 s.c.f.m. and a pressure of 3.4 p.s.i.g., all other conditions remaining the same. It was then found that the gas mixture, after reacting in the melt, yielded the following analysis of major constituents:

H,0:42% (Calculated from a material balance of gas input gas output).

The above analysis indicates that most of the gas has been utilized The above analysis indicates that most of the gas has been utilized in removing oxygen from the copper melt and it can be shown that a gas utilization efficiency approximating 70 percent of the injected methane is achieved. Examples 4-6 clearly show that the rate of reaction is not merely a function of pressure but also a function of temperature. Although it is preferred, from a practical, economic position, to employ relatively high pressure reductant gas at ambient temperatures, the use of relatively low pressures at temperatures up to about the temperature of the molten copper bath also falls within the scope of the present invention.

If the pipe 19 is consumed to the end of its useful life during a refining cycle or becomes so firmly wedged in the pipe 16 due to freezing copper in annular space 31 that further advance into the furnace is impossible, then the expedient as shown in FIG. 5 may be adopted in order to effect a temporary repair. The hose 23 is disconnected from the inner pipe 19 and the tee 20 removed. A three-quarter-inch stainless steel pipe 32 is inserted into pipe 19 to extend beyond the hot wall face 27 into the furnace. A smaller tee 33 is then screwed onto pipe 32 and connected, by suitable adapters to hose 33. The refining can then proceed with only minimal delay and it has been found that the reduced gas flow resulting from the smaller diameter pipe can be compensated by the higher pressure which can be achieved.

When it becomes necessary for a tuyere to be extracted from the furnace, a crane is required to pull out the pipe 19. It is desirable that the direction of pull should be along the centerline of the pipe and with a converter aisle crane this is difficult to achieve. The expedient shown in FIG. 6 overcomes the attendant problems. An arm 34 is pivotally mounted on the furnace shell 1 by lugs 35 and pivot pin 36. The arm 34 consists of two concentric pipes 37 and 38 which slide freely together and are provided with paired holes 39 into which a pin 40 may be inserted to lock said pipes together at any desired length. A special clevis 40 is welded at the free end of arm 34 and includes two eyes through which are attached a short chain 41 and a loop 42. Chain 41 has a hook 43 attached to its end for engagement with a loop 44 and adapter 45 which in turn is screwed onto pipe 19. Loop 42 receives crane hook 46. In use, arm 34 is adjusted to the desired length and the crane pulls the pipe 19 out of pipe 16 for a few inches. The direction of pull changes slowly as the pipe 19 emerges and the length of arm 34 is adjusted, as described by means of pin 40 and holes, this extractor can be used for any of pipes l6, l9 and 32 by selection of suitable adapters 45.

We claim:

1. An apparatus for introducing gas under high pressure into a furnace comprising:

a. an outer highly heat resistant metal pipe secured to a refractory lining of said furnace and having a length sub stantially the same as the thickness of said lining;

b. an inner pipe of highly heat resistant metal slidable within said outer pipe and extending beyond said outer pipe at both its ends;

c. a layer of refractory material disposed between said inner and outer pipes which is composed and secured to ensure a close fit between said pipes and to inhibit fusion therebetween;

d. said pipes being so arranged as to prevent undesirable blow back to the outside of said furnace of gas under high pressure;

e. said apparatus including means adapted to connect a gas supply to the outer end of said inner pipe.

2. The apparatus as defined in claim 1 wherein said inner pipe is so structured and dimensioned as to provide means for directly connecting said inner pipe to a source of gas said inner pipe being shaped and dimensioned to provide conduit means for transmitting said gas into said furnace.

3. The apparatus as defined in claim 1 wherein said layer of refractory material is coated on the outer surface of the inner pipe.

4. An apparatus as claimed in claim 1 wherein said inner pipe is steel.

5. An apparatus as claimed in claim 1 wherein said outer pipe is fabricated from stainless steel.

6. In a rotary copper refining furnace the improvement comprising:

a. an outer highly heat resistant metal pipe of substantially similar length to the thickness of a refractory lining in said furnace and secured thereto;

to prevent said inner pipe from sliding out of said furnace. 7. An apparatus as claimed in claim 6 wherein said pipes are stainless steel.

8. An apparatus as claimed in claim 7 wherein a stainless steel tip is welded to the inner end of said inner pipe.

9. An apparatus as claimed in claim 6 further including a means to extract said pipes. 

2. The apparatus as defined in claim 1 wherein said inner pipe is so structured and dimensioned as to provide means for directly connecting said inner pipe to a source of gas said inner pipe being shaped and dimensioned to provide conduit means for transmitting said gas into said furnace.
 3. The apparatus as defined in claim 1 wherein said layer of refractory material is coated on the outer surface of the inner pipe.
 4. An apparatus as claimed in claim 1 wherein said inner pipe is steel.
 5. An apparatus as claimed in claim 1 wherein said outer pipe is fabricated from stainless steel.
 6. In a rotary copper refining furnace the improvement comprising: a. an outer highly heat resistant metal pipe of substantially similar length to the thickness of a refractory lining in said furnace and secured thereto; b. an inner pipe of highly heat resistant metal slidable into said outer pipe and extending beyond said outer pipe at both of its ends; and c. means adapted to connect a gas supply to the outer end of said inner pipe; d. means to prevent said inner pipe from sliding when said furnace is rotated. e. said sliding prevention means includes a bar to prevent said inner pipe from sliding into said furnace and a chain to prevent said inner pipe from sliding out of said furnace.
 7. An apparatus as claimed in claim 6 wherein said pipes are stainless steel.
 8. An apparatus as claimed in claim 7 wherein a stainless steel tip is welded to the inner end of said inner pipe.
 9. An apparatus as claimed in claim 6 further including a means to extract said pipes. 